It seems that someone turned off the Internet in Syria. A U.S.-based network security firm said in a statement that Syria basically disappeared from the Internet at 12:26 p.m. local time on Nov 29. Rebels blamed the government; the government denied that there was a nationwide outage.

Early last year Egypt and Libya’s Internet were disabled during the height of civil unrest — and given the integral role that the Internet and Twitter have played in organizing activists, it seems likely we'll hear about more instances of Internet shut-offs in the future.

But could it happen in the U.S.?

Iljitsch van Beijnum explains in Ars Technica that in the Middle East and Europe, almost all interconnection happens in the capital of a country — so killing the connections between ISPs wouldn't be too hard. But the U.S. is so much larger and traffic volumes are so immense, that large networks interconnect in at least 20 separate cities, not just one central capital. Numerous intercontinental sea cables land in the Boston, New York, Washington D.C., Miami, Los Angeles and Seattle, which would make it difficult to kill the connections between ISPs.

Some kind of "Internet kill switch" isn’t really a reality, since shutting down the international connections alone would require a tremendous amount of manual work. Van Beijnum's verdict is that it would be "surprisingly hard to kill. It can be done, however, if you're a government and you try really, really hard."

But as David Clark, an MIT computer scientist whose research focuses on Internet architecture and development, puts it: "Whether or not other governments — for example, the U.S. government — are able to shut down the Internet is a regulatory question." He says, "In a time of crisis, does a government have the powers to compel the ISPs to take such an action?" In the U.S., the answer is no — not only does President Barack Obama, or any president, not have access to a physical "switch" that turns off the Internet, he also has no control over ISPs.